In recent years, the substantial increases in the costs of handling and storage of gaseous materials has created an incentive for improved methods of handling and storage of gaseous materials. The manufacture of highly toxic, corrosive and/or poisonous gases or waste gases has created a serious problem of handling and storage of the materials and/or of disposal of unwanted materials. Environmental problems have been created by the need to find adequate and safe means for handling and storing radioactive atomic energy fuel and fuel waste materials. There has also developed a need in inertial confinement fusion systems for a means of obtaining under high pressure small target fuel materials contained in a material from which they do not diffuse or do not diffuse at a high rate.
Hollow glass microspheres have been used as micro-containers for mixtures of hydrogen isotope gases which were used as laser targets to obtain or attempt to obtain thermonuclear reactions. However, the method of making the glass microspheres, the microspheres themselves and the method of filling the microspheres have several disadvantages. The commercially available glass microspheres are made by grinding glass to a desired particle size and heating the ground particles to a high temperature to "blow" the particles into hollow glass microspheres. The "blowing" gas in the known procedure is gas that had been trapped in the glass during the manufacture of the glass. The microspheres that are obtained are of non-uniform size, shape and wall thickness and have contained in the walls thereof small trapped gas bubbles.
The microspheres that are to be used as laser fuel targets must be of uniform size and wall thickness as a consequence of which only a very small proportion of the commercially produced microspheres can be used, for example, one in a million. Further, the gas used to blow the microspheres must be purged and the desired hydrogen isotope gases introduced into the microspheres. The method now used to introduce the hydrogen isotope gases into the microspheres involves relatively high temperature and very high pressure gas permeation or diffusion techniques. The hydrogen gases under high pressure are made to slowly diffuse through the "pores" of the glass microsphere and displace the internal gas in the microsphere. Cooling the microspheres and maintaining the microspheres under refrigeration can substantially reduce loss of the gases thus compressed into the microspheres. Over a long period of time, however, significant amounts of the compressed gases diffuse out of the microspheres which results in a loss of the hydrogen gases fuel and efficiency of the thermonuclear reaction.
The known methods for producing hollow glass microspheres have not been successful in producing microspheres of relatively uniform size or uniform thin walls which makes it very difficult to produce hollow glass microspheres of controlled and predictable characteristics and quality and strength or at low cost which are capable of containing elevated internal gas pressures without significant pressure loss.
An inherent problem with the known method of making microspheres is that since the glass microspheres had to be sufficiently porous to allow the gases to diffuse into the microspheres some of the pressurized gases will diffuse out of the microspheres. Another problem is that the method is limited to the use of low molecular weight gases for diffusing into the microspheres. There is the additional problem that the prior art pressurized microspheres are required to be maintained under refrigeration to minimize outward diffusion of the pressurized gases.
A serious problem that exists with the known method is that the small gas bubbles that are trapped in the walls of the microspheres during manufacture of the microspheres weakens the microspheres, thus limiting to some extent the amount of hydrogen isotope gases or other gases, that is the pressure of the gases, that can be contained in the microspheres.
The known methods of producing hollow glass microspheres, for example, as disclosed in the Veatch et al U.S. Pat. No. 2,797,201 or Beck et al U.S. Pat. No. 3,365,315, involve dispersing a liquid and/or solid gas-phase precursor material in the glass material to be blown to form the microspheres. The glass material containing the solid or liquid gas-phase precursor enclosed therein is then heated to convert the solid and/or liquid gas-phase precursor material into a gas and is further heated to expand the gas and produce the hollow gas microsphere containing therein the expanded gas. This process is, understandably, difficult to control and of necessity, i.e. inherently, produces glass microspheres of random size and wall thickness, microspheres with walls that have sections or portions of the walls that are relatively thin, walls that have holes, small trapped bubbles, trapped or dissolved gases, any one or more of which will result in a substantial weakening of the microspheres, and a substantial number or proportion of microspheres which are not suitable for use which must be scrapped or recycled. Also, the relatively high cost and the relatively small size of the prior art microspheres has limited their use.
Further, the known methods for producing hollow glass microspheres usually rely on high soda content glass compositions because of their relatively low melting temperatures. These glass compositions, however, were found to have poor long term weathering characteristics and a relatively high mean atomic number.
In addition, applicant found in his initial attempts to use an inert blowing gas to blow a thin molten glass film to form a microsphere that the formation of the glass microsphere was extremely sensitive and that unstable glass films were produced which burst into minute sprays of droplets before a molten glass film could be blown into a microsphere and detached from a blowing nozzle. There was also a tendency for the molten glass fluid to creep up the blowing nozzle under the action of wetting forces. Thus, the initial attempts to blow hollow glass microspheres from thin molten glass films were unsuccessful.
In addition, in some applications, the use of low density microspheres presents a serious problem because they are difficult to handle since they are readily elutriated and tend to blow about. In situations of this type, the filamented microspheres of the present invention provide a convenient and safe method of handling the microspheres.